Intermittent Missfire

[gamorg02]

i hear ya dave... you start looking for problems that weren't/aren't there there!

 

[Akatora]

Yeah, the pick-ups seem to be ok.

The steady 147 ohm is not that far - remember that the resistance should grove when the coil gets hotter, and the specified values were for 20 degr. C. Especially if that's the situation for all of them. It's not likely that both pick-ups would have the same problem same time.


Next better to confirm / rule out the possibility of ignition HT coils, plug leads and plugs by measurements and / or exchange method.

- First find out, which cylinder(s) doesn't provide spark. This can be quickly done by taking one extra plug and a piece of steel wire. Now disconnect one of the spark plug caps from the plug and connect the extra plug into the cap. Then connect the piece of wire to the plug thread and the other end to the frame bolt or somewhere it gets well grounded.
- Start the engine and see if there is spark in your "extra plug".
- Check each cylinder by turns.
- When the problematic cylinder is clear, conduct a measurement by multimeter for the coil of the problematic cylinder. Check the resistance between red/white and orange wires (primary side). It should be around 2.4-3 ohms. Then measure the secondary side by checking the resistance between coil lead and red/white wire. It should be around 10.5-15.8 kilo ohms without plug cap.

You can confirm the result by removing the ignition HT coil and exchanging it with some other cylinder's coil.
- Then check again, if the problem moves with the HT coil or stays in the original place.
- If it stays in the original place, go ahead and check the TCI unit
- If it moves with HT coil, measure the values again and try some different plug lead and plug caps with the coil.


When the HT coils are clarified and if not guilty, continue into TCI.

- First disconnect the joint sockets, both of them, from the TCI unit. Then carefully use suitable brush and maybe some electrical circuit cleaner liquid and brush the connectors clean from the unit side and from the socket side.

- Connect the sockets again into the unit and try if the problem went away.

- If it still exist, see the TCI thing here: http://www.venturerider.org/forum/sh...ad.php?t=10640

Note that the front cylinder HT coils are crossed. Left side provides spark to right side cylinder and vice versa.

If all the cylinders provide good spark, then it is more than likely to be related to intake air leakage or carburation (assuming that the spark is ok for all the cylinders).

Hopefully you can find it out soon!

Regards,

AT

 

[OzDave]

Awesome link! For future folks who are having TCI/CDI problems check out that link above!

Particularly interested in the section regarding pulling the CDI/TCI apart for corrosion and moisture. The Vmax had to put up with a few nights in the rain recently... bit of an issue with a brakefluid spill in the garage chewing through rubber... Could be that some moisture got in there, a bit of corrosion, things heat up and expand and lose contact...

My other problem seems to be that the misfire is worst under load... its a lot like a turbo car blowing out its spark. Its rough as guts when moving, but when I come to a halt its pretty stable. When idling I cant be sure if its misfiring at all, there's a very slight stumbling now and then but I think that's how it's always been...

Gonna pull apart the TCI and inspect it, then check spark...

 

[OzDave]

Okay, another round of testing done. Chilling the TCI had no effect. But...

Is there something special about the front cylinder on the gear shifter side? Because... Checking the spark through the leads, every other cylinder, no effect on the idle a lumpy running on three sound. Then when it came to that cylinder... nothing. Would turn over but wouldn't catch. Spark looked normal when testing it, but with every other cylinder itd keep running on three, that one itd just drop dead.

Fuel flow to that cyclinder seems normal, once i reconnected it had an almighty backfire, so fuel was being sucked in and not ignited while the spark was out... but there's no way the bike could be running on one cylinder... wtf is going on?

 

[Akatora]

Hello,

Ok, so you have now located the problem to be with the no. 2 cylinder (front left side).

Next thing to check is ignition HT coils. They are located nearby the TCI unit. Note that front left side cylinder is controlled by the HT coil that is on the right side and vice versa. The front cylinder coiling is crossed. Rear cylinders are not.

Now, the most simple thing is to exchange the HT coil of no. 2 cylinder and some other cylinder. Then check whether the problem moves together with the coil or stays still in the no. 2 cylinder.

If it moves with the coil, the culprit possibilities are the HT coil, the lead or the plug cap of it.

If it stays in the same cylinder even if you moved the coil, then the possibilities are the TCI unit or the pick-up coil - or the wiring between there. But your pick-up coil measurements suggest them to be good, so they are not now the first suspects.

Better to do the HT coil exchange and see the results...

Cheers!

AT

 

[OzDave]

Arggh this is getting wierder by the second, I've been tearing into the bike trying to pull out each part to bench test. Coil pack to the suspect cylinder is fine, but now the coils for the back cylinders are wierding me out.

Pull the lead off where it goes into the coil on the back gear shifter side and its full of blue goo... odd none of the others had blue goo in there. Have a close look at it, it looks like some kind of paste, like a man made product not a build up, so I'm thinking it might be some kind of conductivity paste or something, but why isn't it on the rest of them... then hook up the multimeter, the front coils holds a steady 13 k-ohm through the secondary coils like the manual says they should.

The back two climb in resistance, and they're all over the shop. Sometimes 700 plus sometimes negative... this really doesn't sound right, so I'm mighty close to throwing in the towel and just buying four COP's but just wanna check if anyone knows whats going on here. I mean the coil packs are disconnected and are being tested independantly, so unless they do a real slow discharge or something I'm guessing they're the problem

 

[Akatora]

Hello,

...calm down, mate...! If you get strange results from measurements, there is probably problem there.

Just back to basics.

1) Don't assume anything
2) Believe in your inspection results

Maybe it's the HT coils and in that case you would solve the problem by just converting them into COPs or just renewing them.

Anyway, as mysterious faults where the cause is unclear are frustrating, I would still confirm the problem the way described in the previous one.

Means to put them HTs back, then confirming with extra plug where the spark problem is. Then exchange the HT coil of the problem area with some other and see whether the problem travels or not. If you do that, you can be quite sure about the reason.

It'll be clarified, sooner or later...

Regards,

AT

 

[OzDave]

It was the blue goo!

Buggered if I know what it was or why it was there, but it was just weirding me out. Ended up pulling the entire front end of the bike to bits trying to trouble shoot it, and when I got to frustrated to continue took a sample of the blue goo inside to experiment on. I dont know what it was, but its resistance would rise and fall with heat. So that got me thinking that probably the reason the coil packs where giving me such weird readings, scraped out as much of the stuff as I could manage and put the bike back together... its not running perfectly, but she's steady and reliable.

So annoyed I pulled an entire bike apart when it was something so simple, but hey, problem solved and it didn't cost me a cent!

So for those in the future suffering misfiring when hot... beware the blue goo!

For those in the present, this is why I hate electrical faults... mechanical and liquid I can understand, but electrical always gets weird... where in the service manual does it say look for blue goo?

 

[Akatora]

Hello Oz,

Did you happen to take any photos? Would be interesting to see...

Regards,

AT